Porous printing cylinder



April 26, 1949- w. c. HUEBNER 2,468,400

POROUS PRINTING CYLINDER Filed May 12. 1945 3 Sheets-Sheet 1 5 77 i 2'0 23 72 Zi 25 70 72 77 www April 26, 1949.

Filed May 12, 1945 w. c. HUEBNER 2,468,400

POROUS PRINTING CYLINDER '3 Sheets-Sheet 2 Zr-Q9. 6.

INVENTOR.

APHl 26, 1949- w. c. HUEBNER 2,468,400

POROUS PRINTING CYLINDER Filed may 12, 1945 :s sheets-sheet 3 mVENToR. 676 479 57 )[ZZzzm jzf'zcaec Patented Apr. 26, 1949 UNITED STATES PATENT oFFicE POROUS PRINTING CYLINDER.v

William C. Huebner, New York, N. Y. Application May 12, 1945, Serial No. 593,449

11 Claims. 1

This invention relates in general to printing processes and apparatus, and in particular tothe provision or use of printing cylinders or elements which, while capable of use in various different printing processes or types of printing apparatus, are especially suitable for use in printing 91'00- esses and apparatus of the nature disclosed in U. S. Letters Patent issued to me and in applications for patent in which ink is transferred from the printing element or surface to the print-receiving medium to make the print thereon by electrostatic, electromagnetic or electronic action without pressure contact of the print-receiving medium with the printing surface.

Heretofore, all printing has been done from surfaces made for use with either relief, planographic or gravure processes of printing in presses specially designed for each different process. In relief and planographic printing, inking rollers are used for applying the ink to the printing areas of the printing elements or surfaces, In gravure or rotogravure printing, the ink is applied, as by rollers, over the entire surface of the printing element and scraped clean from the non-printing areas of the surface by the orthodox doctor blade, which leaves the ink only in the recess or intaglio image-printing areas of the surface. In all of the above mentioned orthodox printing methods, pressure is used for printing or lifting the ink image or impression from the printing surface or printing element to the paper or other print-receiving medium.

There is, in addition, a method or means of applying ink or pigments to material surfaces known as silk screen printing, wherein a silk screen is provided with a mask or masking portions covering portions of the silk screen, and the ink or pigment is daubed through the open 'or unmasked portions of the screen onto the print-receiving medium or surface. In such silk screen printing, the ink or pigment is either applied by hand or by spraying, and the procedure is esseentially a manual process and should not be confused with printing production by high speed processes or presses.

According to my invention forming the subject matter of this application, a printing element, preferably in the form of a tube or hollow cylinder, is employed that is made of material which is porous or permeable by fluid inks, dyes or pigments, and which is provided with a printing surface composed of or comprising non-printing areas that cover or mask portions of the porous printing element and are impervious and block passage therethrough of fluid inks, dyes or pigments, and image-printing or recess areas through which surface portions of the porous or permeable printing element are exposed. The fluid ink, dye or pigment is applied to the inner or undersurface of this printing cylinder or element and issues or is expelled through the pores or permearble material of such exposed imageprinting portions only of the printing surface for transfer therefrom to the printing medium, either with or without contact pressure of the print-receiving medium against the printing surface. The herein disclosed process is therefore especially suited for use in an electronographic printing process or apparatus such as above mentioned, because in such process and apparatus, no pressure is required to transfer the ink or lnk image from the printing surface to the printreceiving medium, since the transfer may be effected by electronic, electrostatic or electromagnetic action, in which, for instance, the ink image may receive an electronic Vcharge of one polarity and the print-receiving medium receive another charge of opposite polarity. Or, the printing or transfer of ink from the printing surface to the print-receiving medium may be effected either with or without a separate transfer charge of electrons at the usual printing line where pressure would be used in orthodox printing presses. The invention, however, is not restricted in application to such printing apparatus but is capable of use in printing apparatus of other types. Furthermore, the invention enables the production of printed matter without the use of rollers or equivalent means for inking the printing surface or element.

One purpose of my invention is to provide a novel printing method and means which are practical, efficient and economical, and also to improve the printed product by the employment of means for utilizing inks, dyes or pigments best adapted for effecting required results and best suited to the particular character of the material to be printed.

Other objects of the invention are to provide a novel printing cylinder or element in the use of which the ink, dye or pigment is expelled orA permeates through the material of the element to the printing surface thereof, as distinguished from being applied to the printing surface, as by means of inking rollers; also to simplify printing processes or apparatus by the elimination of inking rollers and their operating mechanism; also to lower the cost of printing apparatus since the item of inking rollers is a sustantial one in the cost of building, selling and using printing presses of orthodox types; also to avoid the loss of time required in other printing methods of setting the inking rollers and to save the cost of recovering and maintenance of the rollers in proper operative condition.

Another object attained by eliminating the inking roller system is to avoid the hardening, drying or setting of the ink on rollers in multicolor printing where high speed is essential, by elimination of that system entirely.

Still another object is to provide simple means whereby in a multicolor printing process the color for a given printing cylinder can be changed quickly and thus reduce the waiting time for the printing apparatus between runs.

Further objects and advantages of the invention will appear from the following specification of the preferred embodiments of the invention shown in the accompanying drawings, and the novel features of the invention are set forth in the appended claims.

In said drawings:

Fig. 1 is a view, partly in elevation and partly in longitudinal section, of a printing cylinder illustrating one form of apparatus embodying my invention.

Fig. 2 is a view, partly in elevation and broken away in parts, to show different inner portions of a printing cylinder illustrating a slightly diierent form of apparatus embodying my invention.

Fig. 3 is an enlarged, fragmentary, section of the printing cylinder on line Fig. 1.

Fig. 4 is a similar transverse sectional elevation of a. printing cylinder on line 4-4, Fig. 2.

Fig. 5 is a transverse sectional elevation of the cylinder on line 5-5, Fig. 1.

Fig. 6 is a somewhat schematic sectional view showing a means for supplying the fluid ink, dye or pigment to a. printing cylinder.

Figs. 7 and 8 are diagrammatic views illustrating different Ways of using printing cylinders embodying the invention in making prints therefrom.

Fig. 9 is a diagrammatic view illustrating use of al porous or permeable printing element which may be of flat or non-tubular form.

In their preferred embodiments, the printing elements are in the form of printing cylinders. Describing first the printing cylinder as illustrated in the drawings, it comprises an outer tube or hollow cylinder I0 of material of a porous nature, which is permeable by fluid inks, dyes, pigments or printing liquids which may be applied by suitable means to the inner surface of the tube. Arranged concentrlcally within this porous tube Ill is an inner cylindrical tube I I which preferably has liquid flow" channels or grooves in its peripheral surface and is separated from the outer tube by a shallow annular space I2 for application of the ink or liquid to the inner surface of the porous tube. The outer Atube Ill may, for instance, consist of a comparatively thin tube made of suitable clay and baked without glaze to harden it according to the .practice of making unglazed ceramic articles, and the tube may be ground true both inside and outside by suitable grinding means to remove any irregularities and to adapt liquids, such as fluid inks, dyes or pigments to permeate or pass uniformly through the pores of all portions of the material like a filter outwardly from the inner surface thereof. The tube may also be made of other suitable transverse 3-3,

materials, such as plastic materials, so mixed and prepared that they will be porous or permeable and transmit or permit the passage therethrough of liquids with sufficient freedom for the intended purpose of the invention. The inner tube may be made of metal or other suitable solid or impervious material.

As shown, the tubes I0 and II extend between and are supported by opposite circular cylinder heads or end pieces I3 and I4 which are provided with central journals I5 for supporting the cylinder for rotation in suitable bearings, and the cylinder heads are shown as provided with peripheral cap rings I6 having cylindrical anges I1 which are shouldered and extend wit-hin the ends of the outer tube III to form supporting seats for the latter. The opposite ends of the inner tube II may flt between the flanges I'I of the cap rings and annular shoulders I8 on the inner ends of the cylinder heads.

One cylinder head, for instance I3, is provided at its inner end with a cover plate I9 secured to the inner end face of the cylinder head I3, as by screws, and this cover plate of the cylinder head I3 forms the supporting shoulder I8 for the inner tube. This cover plate is of smaller diameter than the internal diameter of the adjacent cap ring I6 so as to form between the periphery of the cover plate and the ring an annular passage or channel 20 at and opposite to the adjacent end of the end inner tube II, and this cylinder head is also provided with a central or axial fluid inlet opening 2| extending through the cylinder head and with passages 22 which weave through the cylinder head and establish communication from central inlet passage ZI to the annular passage 20. The passages 22 can be conveniently machined in the inner face of the body disk of the cylinder head and closed by the cover plate I9 to form internal passages in the cylinder head I3 connecting the inlet opening' 2| with the annular passage 20. Preferably, the opposite cylinder head I4 is provided at the adjacent end of the inner tube II with an annular channel 20a and the outer, peripheral surface of the inner tube II is formedfoigprovided with narrow fluid channels 23 which extend spirally about 1the tube from end to end thereof and communicate at opposite :ends withrthe channels 20 and 20a in the opposite cylinder heads so that huid ink, dye or pigment can readily pass through the passages of the cylinder head I3 into and circulate through the peripheral channels 23 of the inner .tube and the annular space I2 between the inner and outer tubes for applying the fluid ink, dye or .pigment uniformly over the entire inner surface of the outer porous tube for expulsion or permeation through the pores or permeable material of the outer tube. The peripheral channels 23 in the outer tube can be of any suitable shape, but preferably have rounded edges as shown, whichenables them to be more readily kept clean and free of obstructing accumulations.

portions of the masking material which leave the corresponding or registering outer surface portions of the porous tube exposed, so that the fluid ink, dye or pigment can permeate `through the pores of the'tube into and nil these imageforming or printing areas of the' printing surface. The printing surface can be formed, for example, by a glue, albumin, bicromate, photographic or light-sensitive coating on which a photographic printing image is formed, as by exposure of the coating to light through an image negative or positive, or other known methods of exposure to light, and then suitably developing the coating, as by washing with a suitable developing solution to thereby remove or clear away those portions of the coating which were not lighthardened and leave bare the registering surface portions of the porous tube to form the imageprinting areas, while those portions of the coating which are light-hardened remain and mask underlying portions of the porous tube and form the non-printing areas of the printing surface.

In Fig. 1, for example, a fragment of a photographic printing surface is illustrated, containing tone graduations. 21 indicates the usual half tone dots used in the formation of a printing image, and 28 represents a grain process, but the grains and dots are greatly enlarged so that they can be clearly seen in the drawings. However, it is to be understood that gradations of the finest character can be printed by this method, in which the ink is expelled or permeates through the porous printing element, depending on the process employedin making the printing surface for this process of ink expulsion printing. When color photographs are made. the grain structure of the positive or negative ls so arranged that the spaces between the particles provide means for expelling dyes so that color photographs may be printed with liquid dyes upon suitable print-receiving material.

The printing surface, however, may -be formed or provided on the porous or permeable tube in any other suitable manner which will provide impervious masking or non-printing areas 25 and image-forming or image-printing areas 26 through which suitable inks, dyes or pigments can pass or be expelled for transfer to the printreceiving medium. Fig. 2, for example, illustrates more or less diagrammatically another such printing surface.

The printing cylinder as illustrated in Figs. 2 and 4 may be constructed as above described, with the exception that in this modification a layer of absorptive material surrounds the inner cylinder il in the annular space between the inner and outer cylinders. This absorptive covering 29 may be formed by one or more cords of molleton or other suitable absorptive material wound helically on the channeled periphery of the cylinder Il and preferably crossing the surface flow channels thereof, and is adapted to absorb the iiuid ink, dye or pigment delivered, as above explained, to said surface channels or said annular liquid space, and apply the liquid to the inner surface of the porous outer cylinder. This embodiment of the printing cylinder is ybetter suited for the use of thin dyes or colored liquids which flow very freely, and is adapted to ensure a very uniform distribution of the dye or liquid over the whole inner surface of the porous cylinder without permitting a possibly too copious delivery of the thin dye or liquid to the external printing surface of the porousA or permeable cylinder.

The construction of the printing cylinder first described, in which the absorptive covering or layer is omitted, on the other hand, is better suited for the heavier or greasy printing inks or liquids.

The fluid ink, dye or pigment may be supplied to the printing cylinder .by anysuitable means which will insure proper delivery of the liquid to the flow channels of the inner cylinder or annula!- liquid space between the inner and outer cylinders, and through the pores of the outer cylinder to the external printing surface thereof. For instance, as illustrated in Fig. 6, the liquid may be supplied under pressure from a tank 30 through a suitable pipe or hose 3| connected by an ordinary swivel union 32 to the inlet opening 2l of the cylinder head I3. This supply may be regulated by a suitable control valve 33 in the supply pipe and air under pressure may be supplied to the tank through a pipe or connection` 34 for maintaining the liquid under appropriate pressure for insuring its proper delivery to the liquid space ybetween the inner and outer cylinders. This pressure may be regulated in any usual manner, as required, to best suit the particular character of the fluid ink, dye or pigment being used, and the liquid supply tank may be provided with an ordinary gage 35 to indicate the pressure in the tank.

While preferably a cylinder of a construction such as one of those described is employed for delivering and applying the fluid ink, dye or pigment to the inner surface of the porous or permeable printing cylinder or element, it should be obvious that other means for this purpose may be employed. For example, the uid ink, dye or pigment could be applied uniformly on the inner surface of the porous or permeable element, as for example, by a roller arranged within the holow printing-1y cylinder, and provided with an absorptive covering arranged to roll in contact with the inner surface of the porous or permeable printing cylinder for moistening or dampening it, as disclosed in my application for U. S. Patent Ser. No. 574,186, filed January 23, i945.

In case of the use of an ink or pigment of a character which is made more fluent by heating, the printing cylinder may be suitably heated, as by suitable electric heating elements arranged Within the inner tube of the printing cylinder, as illustrated at 36 in Fig. 3. By the use of such heating means, if the ink should become too stiff for proper permeation or expulsion through the porous or permeable material of the tube carrying the printing surface, it can be heated by means of such heating elements to the extent necessary to give the ink the required fluidity.

The printing or -transfer of the image or ink, dye or pigment from the printing surface to the paper or other print-receiving medium can be effected by printing instrumentalities o-f known or suitable types, either with or Without pressure contact of the print-receiving medium with the printing surface. Fig. '7, for example, illustrates diagrammatically a printing apparatus in which the ink or image may be transferred from the printing surface to the print-receiving medium by electronic, electromagnetic or electrostatic action, either with or without actual contact of the print-receiving medium with the printing surface. In this printing apparatus the paper or medium 4U to receive the print may be applied in face to face contiguity with the printing surface, as by a roller 4i between which and the surface of the printing cylinder the print-rethe pressures applied receiving medium, as explained in my beforementioned patents and applications, either with or without the use of means 44 and 45 for charging the ink on the printing surface with electrons of one polarity and charging the printreceiving medium with electrons of opposite polarity. Thus, printing may be achieved by expulsion inking where the ink contacts the printreceiving material 40 held against the printing cylinder, as by a roller, but without pressure, since thin liquids can be discharged by air pressure in the ink supply tank through the cylinder, and where printing pressure is not desirable, the

pigments coming to the surface of the printing cylinder can be ionized by one polarity of an electronic circuit where the electrons are discharged into the ink image and discharged with the ink to the paper, as shown.

In Fig. 8 is illustrated diagrammatically different printing means in which the print-receiving medium is adapted to be held in face to face contact with the printing surface, as by a resilient pressure roller 46 which effects sufficient pressure of the print-receiving medium against the printing surface to lift the ink impression from the printing areas of the printing surface. The pressure, however, would be far less than in orthodox printing presses, and is such as is adapted for use with a tubular porous or permeable printing cylinder or element of the sort herein described.

Fig. 9 illustrates means by which a porous or permeable printing element is employed which embodies the hereinbefore described principle of inking the printing surface by expulsion or passage of the ink through the permeable body of the printing element, but in which the element may be of flat or non-tubular form.

48 indicates the permeable printing element in the form of a flat plate provided with an upper printing surface composed, as before explained, of impervious and pervious areas which respectively form the non-printing and image-printing areas of the printing surface. This permeable element lies on a felt or analogous pad or blanket 49 saturated with the fluid ihk, dye or pigment, within an air-tight chamber formed, as by two sections 50 and 5I of a metal box, between the meeting edges of which is a sealing gasket 52 for making the box air-tight when closed. The paper sheet or print-receiving medium 53 is placed on the printing surface and held in contact therewith by a suitable backing plate 54 within the box, and the ink may be expelled through the permeable printing element and printing surface against the print-receiving medium, as by air under pressure delivered through a pipe or tube 55 to the box chamber beneath the saturated pad 49.

In the printing cylinder as herein disclosed, the porous printing tube is removable from the cylinder head I4, thus adapting its removal for forming the printing coating or surface thereon, as in a suitable coating machine, or for other reasons, such as for cleaning the printing cylinder or for replacing one tube by another one with a printing image for a different color in multicolor printing. In order to properly register the printing images of different tubes, the

cylinder head I4 may be provided with a registering lug or projection 56, Figs-1 8: 2, adapted to seat snugly in a complementary. registering notch 51 in the adjacent end of each printing tube. Ink of one or another color can be supplied to the printing cylinder, as bydisconnecting the supply pipe of a tank containing ink of one color from the cylinder at the swivel union and connecting the cylinder to the pipe from another tank containing ink of another color.

I claim as my invention:

1. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of material permeable by fluid ink and provided with an outer printing surface composed of non-printing areas which are impervious to said fluid ink, and recess areas which form a printing image and leave corresponding outer surface portions of the permeable tube exposed for the passage of the fluid ink into said recess areas through the permeable material of the tube, an impervious cylinder within said outer tube close tothe inner surface of the latter and having in its outer surface channels through which said uid ink can flow for delivery to the inner surface of said permeable tube, and means for supplying said fluid ink to said channels whereby the ink can pass through the permeable material of said tube to said recess printing areas for transfer to a print-receiving medium applied in face to face contiguity to said printing surface of the cylinder.

2. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of material permeable by fluid ink and provided with an outer printing surface composed of non-printing areas which are impervious to said uid ink, and recess areas which form a printing image and leave corresponding outer surface portions of the per-A meable tube exposed for the passage of the fluid ink into said recess areas through the permeable material of the tube, an impenvious cylinder within said outer tube close to but spaced from the inner surface of said permeable tube, and having in its outer surface numerousY narrow flow channels for delivery of the uid ink to the inner surface of said permeable tube, and means for supplying said fluid ink under pressure to said channels, whereby the ink passes through the permeable material of the tube into said recess areas of the printing surface for transfer therefrom to a print-receiving medium applied in face to face contiguity to said printing surface.

3. In a. printing apparatus, a printing cylinder comprising an outer cylindrical tube of material permeableby uid ink and having an exterior printing surface composed of non-printing areas which are impervious to said fluid ink and mask surface portions of said permeable tube, and recess areas which form a printing image and leave corresponding outer surface portions of said permeable tube exposed for the passage of the uid ink into said recess areas through the permeable material of the tube, an inner cylinder having ow channels for the fluid ink in its outer surface and arranged within said permeable tube and separated by a shallow annular space from the inner surface of said permeable tube, absorptive material surrounding said inner cylinder in said annular space and contacting with the inner surface of said permeable tube, and means for supplying the fluid ink to said flow channels, whereby the ink is conveyed by said absorptive material to the inner surface of said permeable tube and is rpermeable through the latter to said recess areas of said printing surface for trans- "9 fer therefrom to a printing medium applied in face to face contiguity to said printing surface.

4. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of material permeable by uid ink and having an exterior printing surface composed of non-printing areas which are impervious to said fluid ink and mask surface portions of said permeable tube, and recess areas which form a. printing image and leave corresponding outer surface portions of said permeable tubes exposed for the passage of the fluid ink into said recess areas through the permeable material of the tube, an inner cylinder having flow channels for the fluid ink in its outer surface and arranged within said permeable tube adjacent the inner surface thereof, a head at an end of said cylinder having channels communicating with said surface flow channels of said inner cylinder, and means for supplying said fluid ink to said cylinder head channels for delivery to said surface channels of said inner cylinder, whereby the fluid ink permeates through said permeable tube into said recess areas of said printing surface for transfer therefrom to a printreceiving medium supported in face to face contiguity to said printing surface.

5. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of material permeable by fluid ink and having an exterior printing surface composed of non-printing areas which are impervious to said fluid ink and mask surface portions of said permeable tube, and recess areas which form a printing image and leave corresponding outer surface portions of said permeable tube exposed for the passage of the fluid ink into said recess areas through the permeable material of the tube, an inner cylinder having fiow channels for the uid ink in its outer surface and arranged within said permeable tube adjacent the inner surface thereof, a head at an end of said cylinder having channels communieating with said surface flow channels of said inner cylinder, and means including an axial swivel union for supplying the fluid ink under pressure to said cylinder head channels for delivery to said surface channels of the inner cylinder, whereby the fluid ink is caused to permeate through said permeable tube into the recess areas of said printing surface for transfer therefrom to a print-receiving medium supported in face to face contiguity to said printing surface.

6. In a printing apparatus, a printing cylinder comprising opposite cylinder heads, an inner cylindrical tube extending between and supported by said heads and having in its outer peripheral surface flow channels for fluid ink extending from the end of said tube, an outer cylindrical tube of porous material which is permeable by fluid ink and is supported by said heads surrounding and adjacent to said inner tube and having an external printing surface composed of non-printing areas which are impervious to said fluid ink, and printing areas which leave corresponding outer surface portions of said porous tube exposed for the passage of the fluid ink through the pores of said tube to said printing areas, one of said cylinder heads having an annular passage oommunicating with said fiow channels of said inner tube at one end thereof, an axial passage and passages connecting said axial and annular passages, and said other cylinder head having an annular passage communicating with the opposite ends of said flow channels of the inner tube, and supply means connected by a swivel union with said axial passage of the cylinder head for 10 delivering fluid ink to said flow channels and the inner surface of said outer tube for passage through its pores to said printing areas of said printing surface.

7. In a printing apparatus, a printing cylinder comprising opposite cylinder heads, adjacent inner and outer cylindrical tubes connected at one end to one of said heads with their other ends removably supported by said other cylinder head, said tubes forming between them space for delivery of fluid ink to the inner surface of said outer tube, said outer tube being of porous material which is permeable by said fluid ink and has an external printing surface composed of nonprinting areas which are impervious to said fluid ink, and printing areas which leave corresponding outer surface portions of said permeable tube exposed for the passage of the fluid ink through the permeable material of the tube to said printing areas thereof for transfer to a print-receiving medium placed contiguous to said printing surface, and means for supplyingsaid fluid ink to said space between said tubes for expulsion through the permeable material of said outer tube to said printing areas of said printing surface.

8. In a printing apparatus, a printing cylinder comprising opposite cylinder heads, adjacent inner and outer cylindrical tubes connecting said heads and separated by a shallow annular space, said inner tube having flow channels for a fluid ink or dye extending lengthwise in its outer surface from end to end thereof, anabsorptive cord winding externally on said inner tube in said annular space in contact with the inner surface of said outer tube, said outer tube being of porous material which is permeable by the fluid ink or dye and has an external printing surface cornposed of non-printing areas which are impervious to said fluid ink or dye, and printing areas forming a printing .image which leave corresponding surface portions of said permeable tube exposed for the passage of said fluid ink or dye through the permeable material of the tube to said printing areas of said printing surface for transfer to a print-receivingmedium, and means for supplying the fluid ink or dye under pressure to said channels for expulsion through said permeable outer tube to said printing areas.

9. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of porous material permeable by fluid inks, dyes or pigments and having an outer printing surface composed of areas impervious to said inks, dyes or pigments, and image-printing areas which are permeable by said inks, dyes or pigments, an impervious cylinder within said outer tube leaving between said inner and Outer tubes restricted space for applying the inks, dyes or pigments to the inner surface of said tube, means for delivering the ink, dye or pigment to said space for passage through the pores of said tube to said image-printing areas of said printing surface for transfer therefrom to a print-receiving medium placed in face to face contiguity to said printing surface, and means within said inner cylinder for heating the inks, dyes or pigments.

l0. In a printing apparatus, a printing cylinder comprising an outer cylindrical tube of material which 1s permeable by liquid and is provided with an outer printing surface composed of areas which are impervious to said liquid and other areas which are pervious for the passage of the liquid through the body pores of said tube to the exterior of said pervious areas, an impervious cylinder located concentricaliy Within said outer tube close. to the inner surface of the latter and having inits outer peripheral surface closely related channels through which said liquid can g 1l. In a printing apparatus, the combinationv of a printing cylinder comprising opposite cylindrical heads, concentric inner and outer cylindrical tubes supported at one end by one of said heads with their other ends removably supported by said other cylinder head, said tubes forming between them a shallow annular space in which fluid ink is confined in contact with the inner surface of said outer tube and is prevented, from admission into the interior chamber of said inner tube, said outer tube being of porous material which is permeable by said fluid ink and has an4 external printing surface composed of non-printing areas which are impervious to said fluid ink, and image-printing areas which are pervious for the discharge of the fluid ink passing thereto through the pores of said outer tube for transfer to a printreceiving medium placed contiguous to said printreceiving surface, said inner tube being impervithe liquid can pass out to said fluid ink, means vfor supplying the fiuid ink to said annular space for expulsion through said image-printing areas of said printing surface, and electrical means including an element located within said inner tube for transferring the fluid ink by electric action from said image-printing areas to the print-receiving medium.

WILLIAM C. HUEBNER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,361,783 Thornton Dec. 7, 1920 1,820,194 Huebner Aug. 25, 1931 1,856,181 Burkholdt May 3, 1932 2,049,495 Frender Aug. 4, 1936 2,267,901 Duncan Dec. 30, 1941 FOREIGN PATENTS Number Country Date 539,188 Germany Nov. 23, 1931 557,565 Germany Aug. 25, 1932 362,889 Great Britain 1932 375,168 Great Britain June 23, 1932 

